We have just come back from a very enjoyable week at Duinrell nr Wassennar. Just north of the Hague.
It does depend on what you want from a site but if you are looking for a good central position for South Holland, lots of facilities then this would be a good choice.
There is an excellent theme park adjacent to the site and one of europe's biggest indoor water parks, so if you have kids it's ideal as the entrance price is included in the pitch fee. I thought the theme park was much better than anything in the UK with lots of rides for younger children as well things for adults and older children
I must admit we didn't take our own caravan as it worked out cheaper to hire a static through Keycamp (something to do with the strange school easter holidays this year i think). As far as I could see, there were 2 touring fields, one very central and rather surrounded by statics, and the other a bit further out (this would have been my choice).
My guess is that the site could be a bit busy and noisy in high season, but off season, if you want lots to do it's a good choice.
It's an easy cycle ride to a lovely sandy beach (about 30mins) or about 5 mins in the car.
Jerry